Method of fabricating a metal pipe with an integrally formed liner

ABSTRACT

A metal pipe and method of forming the same with an integrally formed liner for use in corrosive and abrasive environments is disclosed. The liner is comprised of a relatively thick high density polyethylene which is thermally bonded to the metal pipe. An intermediate co-extruded polymer layer of ethylene acrylic acid and a polyethylene/ethylene acrylic acid blend is applied to the metal pipe facilitate thermal bonding. The intermediate layer is applied to the sheet metal in a pre-treatment process prior to roll forming ribs into the sheet metal. The polyethylene liner is applied after the ribs are formed To provide a smooth, hydraulically efficient surface which is resistent to the corrosive action of sulfuric acid and the like encountered in sanitary applications, as well as abrasion caused by the flow of water-born debris such as dirt and gravel as is encountered in culvert applications. Various means for further securing the polyethylene layer to the metal pipe surface are disclosed.

FIELD OF THE INVENTION

The present invention relates generally to buried pipe for use insewers, storm drains, pen stocks, culverts, and other low headapplications, and more particularly to metal pipe with an integrallyformed liner for use in corrosive and abrasive environments and a methodof fabricating the same.

BACKGROUND OF THE INVENTION

Metal pipe of both corrugated and spiral rib design is widely used fordrainage, culverts and other similar fluid conduits. Althoughsusceptible to abrasion, steel pipe is preferred over concrete pipe andthe like due to its comparatively high strength and low weight. Thesecharacteristics render metal pipe relatively inexpensive to manufacture,ship and handle while permitting its use in applications requiring it tosupport substantial soil overburden. Further, in recent years aparticular spiral ribbed steel pipe has been introduced by W. E. HallCo., of Newport Beach, Calif., the assignee of the subject application,that possesses hydraulic efficiency comparable to more costly concretepipe as well as possesses superior structural capabilities for prolongeduse in buried storm drain applications.

Since metal pipe is susceptible to corrosion, its use has heretoforebeen restricted primarily to culvert and storm drain applications. Insanitary applications, i.e. sewer systems, corrosion causing sulfuricacid is formed from hydrogen sulfide generated by waste products. Suchwaste products and/or acid renders the use of steel pipe in sanitaryapplications impractical since it rapidly deteriorates in the corrosiveenvironment. As such, much heavier and more expensive concrete, linedconcrete and/or vitreous clay pipe has traditionally been utilized forsanitary applications. Thus, although metal pipe is generally preferredbecause of its high strength and relatively low weight and cost, metalpipe has heretofore not been widely used in sanitary applications due toits susceptibility to corrosion.

In recognition of these deficiencies, prior art attempts to allow theuse of concrete pipe as opposed to vitreous clay pipe for large sizesewer applications while reducing the susceptibility to corrosion ofconcrete pipe have included: the installation of a thickcorrosive-resistant plastic liner, and/or forming the inside of aconcrete pipe with additional sacrificial concrete in the crown portionof the pipe.

Such prior art corrosion-resistant liners typically comprise plasticinserts sized to be received within each concrete pipe section. Suchliners are commonly cast within each pipe section. Subsequently afterthe pipe sections have been laid in place, adjacent liners are bondedtogether with the intention of forming a seal to prevent corrosivefluids and gases from contacting the concrete pipe. Although such priorart concrete pipe/plastic liner solutions have proven generally suitablefor large size sewer applications, the inherent high cost of suchsolutions has posed a severe impediment in construction products.Further the useful life of such prior art sacrificial concrete pipesolutions is finite, which requires widespread rehabilitation over timethereby mandating tremendous expense in down line rehabilitation costs.

In recognition of the general inability of metal pipe and concrete pipefor sewer applications, in recent years plastic pipe has been introducedinto the marketplace. Although such plastic pipe withstands degradationcaused by the corrosive environment found in sewer applications, its usehas heretofore been primarily limited to small size sewer applications.In this regard, the structural integrity of plastic pipe is extremelylimited such that in large size applications, the sidewall of suchplastic pipe must be fabricated extremely thick or profiled to enablesuch plastic pipe to withstand compressive forces exerted in burialapplications. Due to the high cost of such plastic material, the use ofsuch plastic pipe in large scale sewer applications has beeneconomically unfeasible. Therefore, in view of the specific factorsencountered in large scale sanitary sewer applications, nearly all suchapplications have utilized costly concrete pipe having a sacrificialwall formed therein which significantly decay over prolonged use andthus will require costly rehabilitation and/or replacement over time.

In contrast to the waste product and/or acid environment encountered insanitary applications, metal pipe utilized for burial storm drainapplications additionally encounters substantial problems associatedwith its operational environment. In relation to burial storm drainapplications, wherein metal pipe is the primary material candidate, longterm exposure of the exterior of the metal pipe within the burialenvironment serves to corrode the exterior of the pipe while water anddebris flowing through the interior of the metal pipe degrades the pipethrough abrasion.

In an effort to prevent such corrosion effects, the interior of metalpipe has been lined with concrete in the hopes that a thicker liningwould be more abrasion resistant and thereby resist deterioration andcorrosion. However, there fails to exist any fail-safe means foranchoring concrete to the interior wall of metal pipe. Consequently,pieces of the concrete lining inevitably become detached from the pipe.When combined with the continual abrading action occurring therein, thisquickly destroys the protective concrete layer. Additionally, concreteis susceptible to cracking and chipping as a result of mishandling,earth movement, and thermal stress. Such cracking and chipping resultsin corrosion of the steel surface in the vicinity of the chip or crack.

An alternative prior art approach to solving the corrosion and abrasiondeficiencies of metal pipe for storm drain applications has been tofabricate the metal pipe from plastic laminated steel sheet material.One such prior art product is known as Black-Klad™, a product of InlandSteel Company of Chicago, Ill. Prior to rolling the steel sheet into apipe section, one surface, i.e. that surface which forms the inner pipesurface, is laminated with a polymer material such as a polyethylenecompound. The thickness of such lamination is limited to approximately0.010 inch and is intended to resist degradation caused by corrosion andabrasion. However due to the comparatively thin thickness layer ofplastic laminant, the laminant tends to wear through due to abrasionfrom sand, rocks, etc. and thereby expose the metal surface below.Further, during the pipe formation process, the thin laminant oftentimesis damaged due to metal cold roll forming procedures.

Attempts to apply thicker laminations to such prior art products haveheretofore resulted in greater blistering and separation of the polymercompound from the metal pipe particularly when the pipe is exposed toflow applications. As such, the application of a protective polymerlayer to metal pipe has heretofore been rendered ineffective.

Therefore because the prior art interior lining of metal pipes haveproven susceptible to abrasion and corrosion, and since abrasionresistant inert linings such as those constructed of concrete or aninert polymer material have failed to remain effectively anchored to themetal pipe walls, metal pipe has heretofore been unacceptable for use insanitary applications such as sewer drains.

As such, there exists a substantial need in the art for a sufficientlythick coating or lining which may be securely applied to metal surfacesto maintain the integrity thereof when the metal pipe is placed in acorrosive environment and to remain thereon without blistering duringthe pipe formation process. Further, there exists a substantial need inthe art for an improved metal pipe with an inert protective liningconstructed of a polymer material such as polyethylene which wouldresist the attack of sulfuric acid as well as resist other forms ofcorrosion encountered in sewer application.

SUMMARY OF THE INVENTION

The present invention specifically addresses and alleviates the abovereferenced deficiencies associated in the prior art. More particularly,the present invention comprises a metal pipe with an integrally formedliner for use in corrosive and abrasive environments. In the preferredembodiment of the present invention, the liner is comprised of 0.050 to0.125 inch thick high density polyethylene which is securely bonded tothe metal pipe during fabrication of the metal pipe. However, otherpolymers having corrosion resistant properties similar to polyethyleneare likewise contemplated herein.

The liner is formed by applying a thin co-extruded film of ethyleneacrylic acid and a polyethylene/ethylene acrylic acid blend to the metalpipe surface and subsequently extruding a comparatively thick layer ofhigh density polyethylene thereover. The co-extruded film is applied ina pre-treatment process to the sheet metal, prior to roll formingcorrugations or ribs in the sheet steel. The final relatively thick highdensity polyethylene layer is applied after the corrugations or ribs areformed in the sheet metal and either prior to or subsequent to helicallywinding and forming the sheet steel into pipe sections. The co-extrudedfilm is specifically formed to securely adhere to the surface of thesheet metal and provide an upper film or layer suitable for subsequentthermal bonding of a relatively thick layer of high densitypolyethylene. As such, the co-extruded film serves as a strong adhesivewhich chemically bonds to the metal pipe and additionally forms apolyethylene base material suitable to enable the subsequent applicationof a relatively thick layer of high density polyethylene thereto. Assuch, present invention provides a smooth, hydraulically efficientinterior surface which is resistent to the corrosive action of sulfuricacid and the like as is typically encountered in sanitary applications.It is also highly resistant to abrasion caused by the flow of water-borndebris such as dirt and gravel as is encountered in culvertapplications.

The process of forming the metal pipe of the present invention commenceswith the steps of prewashing the sheet metal to remove any residual oiland dirt. The sheet metal is subsequently bathed in an alkaline solutionto remove chromates and then rinsed. The alkaline bath and rinse arepreferably repeated and the sheet metal is then etched with an etchantand then dried. Optionally, a primer coat of an adhesive may be thenapplied and the sheet metal is heated to cure for particularapplications. Preferably, a co-extruded polymer layer of ethyleneacrylic acid and polyethylene/ethylene acrylic acid blend issubsequently applied over the metal or if used the primer coat to whichit adheres. Subsequently, the pre-treated metal sheet is cooled andcoiled and then formed by conventional techniques to includecorrugations or ribs.

Subsequently, the pre-treated and corrugated sheet metal is heated and amolten layer of polymer such as high density polyethylene is extrudedunto the pre-treated sheet metal typically having a thickness ofapproximately 0.050 to 0.125 of an inch. Due to the polyethylene beingapplied at an elevated plasticized temperature, it securely thermallybonds to the co-extruded film layer previously applied to the sheetmetal to provide a composite corrosion and abrasive resistant pipe. Inthe preferred embodiment, the application of the relatively thick, highdensity polyethylene layer may be applied prior to forming thecorrugated sheet metal into pipe lengths or alternatively justsubsequent to forming into pipe lengths. Subsequently, the pipe sectionsare cooled and cut into desired lengths using conventional techniques.Although disclosed in relation to specific application to pipe formingapplications, the present invention is additionally applicable to othermetal forming applications wherein chemical resistance of the fabricatedmetal product is required.

In addition to being thermally bonded to the co-extruded film layer, therelatively thick, high density polyethylene layer may be further securedto the sheet metal via the use of anchors captured within the taperedchannels of the pipe and attached to the high density polyethylenelayer.

Various means for attaching the anchor to the high density polyethylenelayer are contemplated. The high density polyethylene layer may beforced along with the anchor into the tapered channel such that the highdensity polyethylene layer substantially surrounds the anchor and iscaptured within the tapered channel. The anchor is preferably comprisedof a compressible polymer material such that it may be forced throughthe narrow opening of a tapered channel and then expand such that itremains captured therein. Optionally, the anchor may comprise a hollowcenter extending substantially the entire length thereof to facilitatesuch compression. Alternatively, the anchor may comprise a high densitypolyethylene core substantially surrounded by a low linear densityPolyethylene covering.

Alternatively, the anchor may first be disposed within the taperedchannel and then the high density polyethylene layer applied to theco-extruded film layer as previously described. The anchor is thenbonded or welded to the high density polyethylene layer. Those skilledin the art will recognize that various means, i.e. thermal bondingand/or the use of chemical adhesives or bonding agents, are suitable forattaching the anchor to the high density polyethylene layer.

Alternatively, a layer of polyethylene may be attached to the anchorprior to the insertion of the anchor into the tapered channel such thata portion of the polyethylene layer extends outward through the openingin the tapered channel whereby it may be thermally or adhesively bondedto the high density polyethylene layer.

Alternatively, the anchor may be formed to have an integral portionwhich extends through the opening of the tapered channel and to whichthe high density polyethylene layer may be thermally or adhesivelybonded.

Alternatively, the anchor may be disposed within the channel prior toforming the tapered sides of the channel wherein a narrowed opening isformed. The use of a non-compressible anchor material is thusfacilitated and the likelihood of the anchor being undesirably pulledthrough the opening of the tapered channel is mitigated.

Alternatively, a non-tapered or rectangular channel may be provided anda complementary shaped anchor disposed therein prior to the applicationof the relatively thick, high density polyethylene layer. Therectangular anchor may be wound into the channel in such a manner thatit resists removal from the channel. For example, a substantiallystraight anchor material may be bent during the insulation process suchthat the tendency of the material to straighten forces it outward andthus deeper into the channel, thereby maintaining its position therein.

Thus, various methods are provided whereby the relatively thick, highdensity polyethylene layer may be securely attached to the inner wallsof sheet metal pipe to prevent delamination or blistering of therelatively thick, high density polyethylene layer. The use of anchors asdiscussed above thus further increases the life and reliability of themetal pipe with integrally formed liner of the present invention andalso expands the potential applications of such pipe by reducing thepipe's susceptibility to harsh environments such as those encountered insewer and culvert applications.

These, as well as other advantages of the present invention will be moreapparent from the following description and drawings. It is understoodthat changes in the specific structure shown and described may be madewithin the scope of the claims without departing from the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the exterior of a length of pipeconstructed in accordance to the present invention;

FIG. 2 is an enlarged cross-sectional view of the pipe wall of FIG. 1taken about lines 2--2 of FIG. 1;

FIG. 3 is a flow diagram of the method of forming metal pipe with anintegral liner of the present invention;

FIG. 4 is a perspective view of the apparatus for forming the metal pipewith an integrally formed liner of the present invention;

FIG. 5 is an enlarged perspective view of the pipe former of FIG. 4;

FIG. 6 is an enlarged sectional view of the sheet metal after the ribshave been formed but prior to crimping;

FIG. 7 is a sectional view depicting the crimping lock seam process;

FIG. 8 is a sectional side view depicting the blending of the liner overthe crimped look seam;

FIG. 9 is a flow chart of the pre-treatment, pre-coating process forbonding the co-extruded film layer to the sheet metal;

FIG. 10 is an enlarged cross-sectional view of a portion of the linerand steel pipe showing the resultant co-extruded film layer and highdensity polyethylene layer liner formed on the interior of the pipelayer.

FIG. 11a is a cross sectional side view of a tapered channel having asolid anchor comprised of a single material disposed therein wherein therelatively thick, high density polyethylene layer has been forced intothe tapered channel along with the anchor;

FIG. 11b is a cross sectional side view of a tapered channel having ananchor comprised of a high density polyethylene core and low lineardensity polyethylene covering disposed therein wherein the relativelythick, high density polyethylene layer has been forced therein as inFIG. 11a;

FIG. 11c is a cross sectional side view of a tapered channel having ahollow anchor disposed therein wherein the relatively thick, highdensity polyethylene layer has been forced therein as in 11a;

FIG. 12 is a cross sectional side view of a tapered channel having ananchor disposed therein wherein the anchor has been bonded to therelatively thick high density polyethylene layer;

FIG. 13 is a cross sectional side view of a tapered channel having ananchor disposed therein and having a polymer layer substantiallysurrounding the anchor and extending from the opening of the taperedchannel such that the relatively thick high density polyethylene layeris bonded thereto;

FIG. 14 is a cross sectional side view of a tapered channel having anintegral anchor and attachment member wherein the anchor is disposedwithin the tapered channel and the attachment member extends through theopening thereof such that the relatively thick high density polyethylenelayer attaches thereto;

FIG. 15 is a cross sectional side view of a non-tapered channel;

FIG. 16 is a cross sectional side view of a non-tapered channel havingan anchor disposed therein;

FIG. 17 is a cross sectional side view of the channel and anchor of FIG.16 after the side walls of the channel have been tapered to capture theanchor therein; and

FIG. 18 is a cross sectional side view of a non-tapered channel having arectangular anchor disposed therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description set forth below in connection with the appendeddrawings is intended as a description of the presently preferredembodiment of the invention, and is not intended to represent the onlyform in which the present invention may be instructed or utilized. Thedescription sets forth the functions and sequence of steps forconstructing and utilizing the invention in connection with theillustrated embodiments. It is to be understood, however, that the sameor equivalent functions and sequences may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

Although not by way of limitation, the process and apparatus of thepresent invention is well suited for use on helical spiral ribbed metalpipe such as that disclosed in U.S. Pat. No. 4,838,317 issued to Andreet al. and assigned to the subject assignee W. E. Hall Co. In thisregard, the process and apparatus of the present invention shall bedescribed in relation to the fabrication of such helical spiral ribbedmetal pipe. However, those skilled in the art will recognize that theteachings of this invention are applicable to other metal pipestructures as well as other metal sheet products desired to withstandcorrosive environments.

Referring now to FIGS. 1 and 2, the improved pipe of the presentinvention is depicted generally comprised of a metal, preferably steel,spiral ribbed pipe 10 having externally extending ribs 12 formedthereon, lock seams 14, and an integrally formed polyethylene liner 16.Voids 18 are preferably formed between the liner 16 and the sheet steelof which the pipe 10 is formed as will be explained in more detailinfra.

Referring now to FIG. 3, an overview of the process of forming the metalpipe 10 with an integrally formed liner 16 of the present invention isprovided. The process generally comprises pre-treating sheet metal suchas steel to have a thin co-extruded polymer layer formed thereon andcoiling the same for further fabrication. The pre-treated sheet metal 11is then uncoiled via an uncoiler 20, and ribs and/or corrugations andseams 14 (as shown in FIGS. 1 and 2) are formed thereon with a profileroll former 22 (as shown in FIG. 4). Subsequently the pretreated andpreformed sheet metal 11 may be cleaned and heated 24. A sheet extruderand laminator 26 provides hot extrudate polymer preferably high densitypolyethylene to the upper surface of the sheet metal. The laminatorpresses the hot extrudate into contact with the upper pre-treatedsurface of the sheet metal, thermally bonding it to the co-extruded filmlayer. The pipe and liner are then cooled 28 prior to being received bythe roller and pipe former 30 which forms the flat sheet metal into ahelical pipe section and crimps the seams 14 together to form awatertight seal. A cutter 32 then outs sections of pipe to a desiredlength.

The steps of forming the ribs 12 and seams 14 with the profile rollformer 22 and of forming the flat sheet metal into a helical pipesection with pipe former 30 are thoroughly disclosed in U.S. Pat. No.4,838,317, issued to Andre, et al., the disclosure of which is expresslyincorporated herein by reference. However, other conventional metal pipefabrication techniques as well as other fabricated metal products arecontemplated herein.

As best shown in FIGS. 1 and 2, the metal pipe 10 having an integrallyformed liner 6 of the present invention includes a channeled walldefining a plurality of outwardly projecting structural ribs 12 and ahydraulically efficient interior surface. The ribs 12 are preferablyformed in a helical configuration and the channels 14 which are formedinteriorly thereof are generally formed having either a square orgenerally rectangular cross section and are open along the interiorsurface of the pipe.

Referring now to FIG. 9, the detailed steps of the pre-treatment process19 utilized prior to forming the sheet metal 11 into pipe sections 10 isdescribed. Those skilled in the art will recognize that the sheet metalis fabricated in elongate lengths that are coiled for ease in subsequentforming processes.

The initial pre-treatment process 19 is initiated by a pre-wash 62 beingperformed on the sheet metal typically galvanized sheet steel to removeany residual oil and/or dirt from the upper and preferably lower surfaceof the sheet metal 11. This step may consist of processes well known inthe art such as the application of a detergent, scrubbing with rollerbrushes, and rinsing with water.

The sheet metal 11 is then subjected to an alkaline bath 64 to loosenand remove chromates formed upon the surface thereof. The alkaline bath64 is followed by a rinse 66 which may be comprised of a buffer orneutralizing acid. The alkaline bath 64 and rinse 66 are preferablyrepeated 68 and 70 to ensure adequate removal of chromates. After thealkaline baths 64 and 68 and the rinses 66 and 70, the sheet metal issubsequently subjected to an etchant such as a Parker Bonderite 1303enchant to roughen its surface and prepare it for the application of aprime coat or layer. Next the sheet steel is dried 74 and a prime coat76 may be applied thereto. The prime coat preferably comprises a thinlayer (approximately 1 to 2 mils.) of ethylene aorylio acid which isapplied to the etched surface of the sheet metal 11. Optionally, afterapplication, a primer coat 76 such as an adhesive may be applied andcured with heat to securely bond the primer coat 76 to the etchedsurface of the sheet metal 11. In most instances however, the primercoat 76 may be eliminated as indicated in phantom lines in FIG. 9.

Subsequently, the etched sheet metal 11 is heated 78 to approximately400° F. and a relatively thin, continuous, planar co-extruded polymerlayer is applied to the sheet metal 11. As best shown in FIG. 10, theco-extruded polymer layer is preferably formed having a thickness ofapproximately 10 mils. and is formed having a lower laminant layer 81 anupper laminant layer 82. In the preferred embodiment, the lower laminantlayer 81 is formed of an ethylene acrylic acid which comprises anadhesive which securely bonds the co-extruded laminant 80 to the sheetmetal 11 via direct contact with the sheet metal 11 or contact with theprime coat 76 applied to the sheet metal 11. The upper laminant layer 82is preferably composed of a polymer/ethylene acrylic acid blend having aconcentration of between 70% and 98% ethylene acrylic acid and 2% to 30%polymer such as an olefin which crosslinks with the polyethylene linerto be later applied to the sheet 11. As will be explained in more detailinfra, the co-extruded layer 80 therefore provides a lower adhesivelayer 81 adapted to securely bond the co-extruded layer 80 to the sheetmetal 11 and an upper polymer containing layer 82 which serves as a basematerial to allow thermal bonding of a subsequent polymer to the upperlayer 82 of the co-extruded layer 80. Although not be way of limitation,in the preferred embodiment, the co-extruded layer 80 comprises apolymer co-extruded layer such as that manufactured by Dow ChemicalCompany under the trademark PRIMACORE D.A.F. 624.

In the preferred embodiment, the co-extruded polymer layer 80 is appliedto the sheet metal 11 at an elevated temperature of approximately 400°F. and is pressed tightly thereupon by way of a conventional roller 83.Subsequently, the sheet metal 11 having the co-extruded polymer layer 80applied thereto is cooled 84 and subsequently recoiled 85 for later usein the pipe fabrication process. In the preferred embodiment it iscontemplated that the pre-treatment process is facilitated on both theupper and lower surfaces of the sheet metal 11 with the lower surfacetreatment providing additional corrosion protection for the soil side ofthe resultant pipe. However the lower side may alternatively be coatedwith conventional films such as epoxy for cosmetic purposes.

Referring now to FIGS. 4 and 5, the process of forming the metal pipe 10with integrally formed liner 16 of the present invention is illustrated.As shown, the pre-treated sheet metal 11 previously disposed in a coil30 is mounted upon a conventional uncoiler 20. The uncoiler 20facilitates the uncoiling of the pre-treated sheet metal 11, having theco-extruded polymer layer 80 disposed upon the upper surface thereof.The pre-treated sheet metal 11 passes through a profile roll former 22having a plurality of form rolls 32 which progressively form the ribs 12(as shown in FIG. 1) and edge seam members 54 and 56 (as shown in FIG.6) within the sheet metal 11. It should be noted that the formation ofthe ribs 12 comprises the major cold forming procedures for the pipe 10and is facilitated on the pre-treated sheet metal. As such thesubstantial tensile and compressive forces exerted in the cold formingprocess are accommodated by the relatively thin co-extruded polymerlayer 80 without cracking and/or blistering. Upon exiting the profileroll former 22, the sheet metal 11 enters a cleaner/heater 24 whichprepares the upper surface of the sheet metal 11 for the subsequentthermal bonding of the relatively thick polymer layer, preferably highdensity polyethylene thereto. Preferably the cleaner/heater 24 elevatesthe temperature of the sheet metal 11 and the co-extruded polymer layer80 disposed thereon to approximately 100°-140° F. and not to exceed 180°F. such that the later applied substantially pure polyethylene layerwill more readily thermally bond thereto.

A conventional plastic sheet extruder 26 having a screw assembly 34,extruder head 36, and a laminator 38 is preferably utilized to apply arelatively thick layer of polymer, preferably a high densitypolyethylene to the pre-treated and pre-formed sheet metal 11. As iswell known, the screw assembly 34 heats, plasticizes, and supplies aquantity of high density polyethylene to the extruder head 36. Theextruder head 36 forms the polyethylene into a continuous planar layer40 preferably having a thickness of approximately 0.050 to 0.125 of aninch which is applied to the upper surface of the co-extruded polymerlayer 80 disposed upon the sheet steel 11. In the preferred embodimentthe polyethylene layer 40 is extruded unto the co-extruded polymer layer80 at a temperature approximately 400° F. A laminator roller preferablycomprising a chilled roller 38 subsequently presses the hot extrudatepolyethylene layer 40 into contact with the co-extruded polymer layer 80and the formed and cleaned sheet metal 11. Due to the high densitypolyethylene layer 40 being applied to the upper surface of thepre-treated sheet metal 11 at an elevated plasticized temperature, astrong thermal bond is facilitated between the high density polyethylenelayer 40 and the polymer constituent existing in the upper layer 82 ofthe co-extruded polymer layer 80 disposed upon the sheet metal 11. Assuch, a polymer to polymer thermal bond is achieved which securelyaffixes the high density polyethylene layer 40 to the pre-treated andpre-formed sheet metal 11. The resulting laminated sheet metal 11 maythen be further cooled with blown air or water prior to being formedinto a helical pipe section 46.

After application of the high density polyethylene layer 40 to thepre-treated sheet metal 11, the resultant metal/polyethylene laminatepossesses a cross sectional configuration depicted in FIG. 6. As shown,the high density polyethylene layer 40 extends in a thermally bondedgenerally contiguous orientation over the upper surface of the sheetmetal 11 and preferably overlaps the female edge seam 54 and male edgeseam 56 formed on opposite edges of the sheet metal 11. Additionally, tofacilitate superior hydraulics for the resultant pipe 10, the layer 40preferably bridges over the channel formed by the rib 12 of the sheetmetal 11 forming voids 18 rendering a generally planar configuration tothe high density polyethylene layer 40. Those skilled in the art howeverwill recognize that the layer 40 may alternatively be pressed into thevoids 18 to be generally contiguous with the rigs 12 or alternativelythe voids 18 may be filled with a polymer material if desired during thelamination process.

Subsequently, the thermally bonded metal/polyethylene sheet 44 is passedinto a crimp/forming roller 50 which helically winds and crimps the maleand female edge seams 56 and 54 into a lock seam which forms theresultant pipe length 46. The action of the crimping/forming roller 50is depicted in FIG. 7. As shown in FIG. 7, the crimping/forming rollers50 crimps adjacent edge seam members 56 of laminated sheet metal 44together by forcing male seam member 56 into the female seam member 54of an adjacent turn as the sheet steel 44 is rolled helically and thenbending both male 56 and female 54 seam members into laminarjuxtaposition with the adjacent laminated steel sheet 11.

The crimping action of crimping/forming rollers 50 causes the highdensity polyethylene laminate 40 to be moderately displaced i.e. migrateaway from the crimped edge seams 56 and 54, thereby pooling i.e. formingdisplaced polymer portions 59 adjacent the lock seam.

So as not to affect the hydraulic efficiency of the interior of the pipe10, in the preferred embodiment, an additional roller 52 is providedwhich extends outwardly beyond the lock seam formed by the crimped edgeseams 56 and 54 which causes the displaced polymer portions 59 to beblended over forming a generally smooth configuration to the polymer 40as shown in FIG. 8. Subsequently, the polymer layer 40 may be cooled andsubsequently cut to desired lengths via a conventional band saw,abrasive wheel, plazma, or laser pipe cutter 48.

As will be recognized the resultant pipe section 46 has substantialstructural strength typical of conventional spiral ribbed metal pipe.Further, as shown in FIG. 10, the pipe 10 includes an integrally formedsubstantially pure high density polyethylene liner 16 having sufficientthickness (i.e. approximately 0.100 of an inch) which is capable ofwithstanding corrosion caused by contaminant acids encountered in sewerapplications. Additionally, since the high density polyethylene liner 16is applied integrally to the pipe during the fabrication process andthermally bonded to the co-extruded polymer layer 80 adhered to thesteel pipe 11, delamination, blistering or cracking of the high densitypolyethylene layer 16 is eliminated. Further upon installation of thepipe 10 in sewer applications, adjacent pipe sections may be easilyabutted and joined at their interfaces by utilizing high densitypolyethylene wraps which may be thermally welded/bonded to the highdensity polyethylene liner affixed to the interior of the pipe.

As an additional embodiment of the present invention, it is contemplatedthat the application of the relatively thick polyethylene layer 40 maybe applied to the pre-formed and pre-treated sheet metal 42 subsequentto all structural metal forming operations for the pipe 10. Thisadditional embodiment is illustrated by the phantom lines in FIG. 3wherein the sheet extruder and laminator 26 and subsequent cooling stepis depicted in phantom lines and positioned after the seam roller andpipe formers steps 30. The processes for applying the high densitypolyethylene layer after all pipe forming procedures have been completedis identical to that disclosed hereabove and has the additionaladvantage of avoiding any displacement of the high density polymer layer40 due to the metal fabrication process.

Referring now to FIGS. 11a through 18, the relatively thick layer ofhigh density polymer may be further secured to the sheet metal substrateby capturing a preformed anchor within a tapered channel formed in themetal substrate and attached to the layer of high density polymer. Theanchor is preferably comprised of a polymer material such as highdensity polyethylene and may alternatively be comprised of a highdensity polyethylene core substantially covered by linear low densitypolyethylene. Alternatively, the anchor may comprise a substantiallyhollow core such that it is compressible and may therefore be moreeasily inserted through the narrow opening of the tapered channel. Theanchor is generally disposed within the tapered channel after theco-extruded layer has been applied and the channel has been completelyformed.

With particular reference to FIG. 11a a round anchor 104 is capturedwithin a tapered channel 100. The anchor 104 is comprised of acompressible material and has been forced through the narrow opening 106of the tapered channel 100 after the relatively thick, high densitypolyethylene layer 102 has been applied to the sheet metal surface 103.Thus, a portion 108 of the high density polyethylene layer 102 haslikewise been forced into the tapered channel 100 and is capturedtherein by the anchor 104. In this manner, the high density polyethylenelayer 102 has been further secured to the sheet metal surface 103 tomitigate the probability of delamination or blistering.

With particular reference to FIG. 11b , the anchor 104 may alternativelybe comprised of a high density polyethylene inner core 132 surrounded bya linear low density polyethylene covering 134. The linear low densitypolyethylene outer covering is comparatively more compressible than thehigh density polyethylene inner core 132, thereby facilitatingcompression of the anchor 104 during its insertion through the narrowopening 106 of the tapered channel 100.

With particular reference to FIG. 11c, the anchor 104 may alternativelycomprise a void or hollow core 130 to facilitate compression thereofduring the insertion process.

With particular reference to FIG. 12, the anchor 104 may be insertedinto the tapered channel 100 prior to application of the relativelythick high density polyethylene layer 102 to the sheet metal surface103. The high density polyethylene layer 102 may subsequently be weldedor adhesively bonded to the anchor 104 forming a bond region 110. Thoseskilled in the art will recognize that various welding, e.g. thermal orultrasonic, processes are suitable and that various means of adhesivelybonding the anchor 104 to the high density polyethylene layer 102 arelikewise suitable. The use of adhesive bonding requires application ofthe bonding material to the anchor 104 prior to application of therelatively thick high density polyethylene layer 102 to the steelsurface 103. Attachment of the high density polyethylene layer 102 tothe anchor 104 .thus further secures the high density polyethylene layer102 in place.

With particular reference to FIG. 13, the anchor 104 may be formed tohave a film 112 of polymer, preferably polyethylene, substantiallysurrounding its surface such that the anchor 104 and the surroundingportion of polyethylene film 112 may be inserted into the taperedchannel 100 and a portion 114 of the polymer film 112 may extend throughthe narrow opening 106 of the tapered channel 100 such that the externalportion 114 of the polyethylene film 112 may be bonded to the relativelythick, high density polyethylene layer 102.

With particular reference to FIG. 14, the anchor 104 may be formed tohave an integral external portion 118, preferably connected thereto viaa neck portion 122. Thus, the anchor 104 may be forced through thenarrow opening 106 of the tapered channel 100 such that the neck portion122 extends through the narrow opening 106 and the external portion 118remains disposed outside of the tapered channel 100 such that the highdensity polyethylene layer 102 may be attached thereto.

Referring now to FIGS. 15-17, and alternative method of disposing theanchor 104 within a tapered channel is illustrated. Rather than forgoingthe anchor 104 through the narrow opening 106 of a preformed taperedchannel 100 as illustrated in FIGS. 11a-14, the anchor 104 may bedisposed within the tapered channel 100 prior to the complete formationthereof.

With particular reference to FIG. 15, prior to pinching the sides 126 ofthe tapered channel 100, the channel is initially formed in the crosssectional configuration of a rectangle.

With particular reference to FIG. 16, the anchor 104 is disposed withinthe rectangular channel 124. The anchor 104 may be easily disposedwithin the rectangular channel 124 without the need for compressing theanchor 104 because of the large size of the opening 125 of therectangular channel 124. Thus, a non-compressible anchor may be utilizedto mitigate the probability of the core being inadvertently pulled outof the channel.

With particular reference to FIG. 17, subsequent to disposing the anchor104 within the rectangular channel 124 the sides 126 of the rectangularchannel 124 are pinched together such that a narrow opening 106 isformed thereby, thus capturing the anchor 104 within a tapered channel100. By disposing the anchor 104 within the channel prior to crimpingthe sides 126 thereof, the step of forcing the anchor 104 through thenarrow opening 106 of the tapered channel 100 is eliminated. After beingso disposed within the tapered channel 100, the anchor 104 may be bondedto a subsequently applied layer of high density polyethylene asdescribed above.

Referring now to FIG. 18, an alternative method for capturing an anchorwithin a channel is illustrated. A rectangular non-tapered channel 124receives a complementary shaped anchor 128. The anchor 128 is preferablycomprised of a linear resilient material which tends to maintain astraight configuration such that when bent it attempts to spring backinto a generally straight configuration. The anchor 128 thus tends topush outward against the inner most surface of the bottom 136 of thechannel 124 as it attempts to straighten. That is, the anchor 128, whendisposed within a channel 124 of a pipe is configured as a helix andattempts to straighten out by pushing outwards against the pipe.

The anchor 128 is disposed within the channel 124 prior to applicationof the relatively thick high density layer 102 to the sheet metalsurface 103. After application of the high density polyethylene layer102 the high density polyethylene layer is welded or adhesively bondedto the anchor 128 as described above.

It will be understood that the exemplary steel pipe with integrallyformed liner described herein and shown in the drawings represents onlya presently preferred embodiment of the invention. Indeed, variousmodifications and additions may be made to such embodiment withoutdeparting from the spirit and scope of the invention. For example,various polymer materials having properties similar to high densitypolyethylene and ethylene acrylic acid may be used. In this regard, in abroad sense, the present invention facilitates the use of a relativelythick polymer liner to be disposed upon a metal surface, which polymeris adhered to the metal surface by way of a co-extruded layer having alower most adhesive component and an uppermost polymer/adhesivecomponent which enables the subsequent thermal bonding of the relativelythick substantially pure polymer layer via the constituent polymer layerfound in the uppermost layer of the co-extruded layer.

Additionally, the present invention contemplates the use of affixing aprotective polymer layer to a fabricated product after pre-formingand/or completely forming the fabricated product by pre-treatment of themetal utilized in the fabricated product for subsequent deposition ofthe polymer layer thereto. Also, various metals and alloys havingsufficient structural strength may be utilized as the pipe material.

Furthermore, the polymer laminated metal and method for forming the sameneed not be limited to the fabrication of pipe, but rather may findapplication in many diverse areas such as automotive body sheet metalapplications and the like. Additionally, the anchors 104 need not beround as described and illustrated, but rather may be of any shape andconfiguration wherein they may be forced through the narrow opening ofthe tapered channel and subsequently expand to remain captured therein.Also, the tapered channels 100 need not be generally triangular inshape, but rather may be of any shape and configuration suitable forcapturing the anchor therein and compatible with their use in a metalpipe or other sheet metal structure. Thus, these and other modificationsand additions may be obvious to those skilled in the art and may beimplemented to adapt the present invention for use in a variety ofdifferent applications.

What is claimed is:
 1. A method for forming polymer laminated metal pipecomprising the steps of:(a) providing sheet steel having a co-extrudedpolymer layer of ethylene acrylic acid and polyethylene/ethylene acrylicacid blend applied upon at least one surface thereof; (b) passing saidsheet steel through a profile former to form channels and seam memberstherein; (c) disposing a liner of heated polyethylene in laminarjuxtaposition to said co-extruded polymer layer of polyethylene/ethyleneacrylic acid blend formed upon said sheet steel; (d) applying pressureto said layer of polyethylene to cause said layer of polyethylene tothermally bond to said co-extruded polymer layer ofpolyethylene/ethylene acrylic acid blend, the polyethylene/ethyleneacrylic acid blend of the co-extruded polymer layer bonding to thepolyethylene of the liner so as to securely attach the liner to thesheet steel; and (e) forming said sheet steel into a section of pipe. 2.The method claim 1 further comprising the step of heating at least oneof said co-extruded polymer liner of polyethylene/ethylene acrylic acidblend and said layer of polyethylene prior to the step of applyingpressure to said layer of polyethylene.
 3. The method of claim 1 whereinthe step of forming said sheet steel into a pipe section furthercomprises the steps of:(a) passing said sheet steel by a crimp roller tocrimp adjacent seam members together as said sheet steel is formed intoa helix; and (b) passing said sheet steel by a form roller toredistribute the polyethylene over the seam.
 4. The method of claim 1wherein the step of passing said sheet steel through a profile former isperformed prior to the step of disposing a liner of heated polyethylenein laminar juxtaposition to said co-extruded polymer layer.
 5. Themethod of claim 1 wherein the step of disposing a liner of heatedpolyethylene in laminar juxtaposition to said co-extruded polymer layeris performed prior to the step of passing said sheet steel through aprofile former.
 6. A method for forming polymer laminated metal pipecomprising the steps of:(a) providing sheet steel having a co-extrudedpolymer layer or ethylene acrylic acid and polyethylene/ethylene acrylicacid blend applied on at least one surface thereof; (b) passing saidsheet steel through a profile former to form tapered channels and seammembers therein; (c) disposing a liner of heated polyethylene in laminarjuxtaposition to said co-extruded polymer layer, said liner ofpolyethylene substantially covering said tapered channels; (d) applyingpressure to said liner of polyethylene to cause said layer ofpolyethylene to thermally bond to said co-extruded polymer layer, thepolyethylene/ethylene acrylic acid blend of the co-extruded polymerlayer bonding to the polyethylene of the liner so as to securely attachthe liner to the sheet steel; (e) forming said sheet steel into asection of pipe; and (f) urging an anchor through said liner ofpolyethylene and into said tapered channel such that said liner ofpolyethylene substantially surrounds said anchor such that said liner ofpolyethylene is captured within said tapered channel.
 7. A method forforming polymer laminated metal pipe comprising the steps of:(a)providing sheet steel having a co-extruded polymer layer of ethyleneacrylic acid and polyethylene/ethylene acrylic acid blend applied on atleast one surface thereof; (b) passing said sheet steel through aprofile former to form tapered channels and seam members therein; (c)disposing an anchor within said at least one of said tapered channels;(d) disposing a liner of heated polyethylene in laminar juxtaposition tosaid co-extruded polymer layer; (e) applying pressure to said liner ofpolyethylene to cause said liner of polyethylene to thermally bond tosaid co-extruded polymer layer, the polyethylene/ethylene acrylic acidblend of the co-extruded polymer layer bonding to the polyethylene ofthe liner so as to securely attach the liner to the sheet steel; (f)bonding said liner of polyethylene to said anchor; and (g) forming saidsheet steel into a section of pipe.
 8. A method for forming polymerlaminated metal pipe comprising the steps of:(a) providing sheet steelhaving a co-extruded polymer layer of ethylene acrylic acid andpolyethylene/ethylene acrylic acid blend applied on at least one surfacethereof; (b) passing said sheet steel through a profile former to formtapered channels and seam members therein; (c) disposing an anchorpartially within said tapered channel, said anchor comprising a firstportion which is disposed within said tapered channel and a secondportion which is disposed in laminar juxtaposition to the sheet steelproximate said tapered channel; and (d) bonding a polyethylene linerhaving a thickness greater than said co-extruded polymer layer to saidco-extruded polymer layer and to the second portion of said anchor, thepolyethylene/ethylene acrylic acid blend of the co-extruded polymerlayer bonding to the polyethylene of the liner so as to securely attachthe liner to the sheet steel; (e) forming said sheet steel into asection of pipe.
 9. The method of claim 8 wherein said second portion ofthe anchor comprises a film of polymer substantially surrounding thefirst portion of said anchor and bonded thereto.
 10. The method of claim8 wherein said first and second portions of said anchor are formed as asingle integral unit.
 11. A method for forming polymer laminated metalpipe comprising the steps of:(a) providing sheet steel having aco-extruded polymer layer of ethylene acrylic acid andpolyethylene/ethylene acrylic acid blend applied on at least one surfacethereof; (b) passing said sheet steel through a profile former to format least one channel and seam members therein; (c) disposing an anchorwithin said at least one channel; (d) pinching in the upper portion ofsaid at least one channel to form a taper channel to capture said anchortherein; (e) disposing a liner of heated polyethylene in laminarjuxtaposition to said co-extruded polymer layer; (f) applying pressureto said liner of polyethylene to cause said liner of polyethylene tothermally bond to said co-extruded polymer layer, thepolyethylene/ethylene acrylic acid blend of the co-extruded polymerlayer bonding to the polyethylene of the liner so as to securely attachthe liner to the sheet steel; (g) bonding said liner of polyethylene tosaid anchor; and (h) forming said sheet steel into a section of pipe.12. The method as recited in claim 11 wherein the steps of thermallybonding a liner of polyethylene to said co-extruded polymer layer and ofbonding said polyethylene liner to said anchor are performedsimultaneously.
 13. A method for forming polymer laminated metal pipecomprising the steps of:(a) providing sheet steel having a co-extrudedpolymer layer of ethylene acrylic acid and polyethylene/ethylene acrylicacid blend applied on at least one surface thereof; (b) passing saidsheet steel through a profile former to form tapered channels and seammembers therein; (c) forming said sheet steel into a pipe section suchthat said channels are configured in a substantially helicalconfiguration; (d) disposing an anchor within at least one of saidchannels, said anchor being held within said channel due to the helicalconfiguration of said channel; (e) disposing a layer of heatedpolyethylene in laminar juxtaposition to said co-extruded polymer layer;(f) applying pressure to said liner of polyethylene to cause said linerof polyethylene to thermally bond to said co-extruded polymer layer, thepolyethylene/ethylene acrylic acid blend of the co-extruded polymerlayer bonding to the polyethylene of the liner so a to securely attachthe liner to the sheet steel; and (g) bonding said liner of polyethyleneto said anchor.
 14. The method as recited in claim 13 wherein saidanchor conforms generally in shape to the shape of said channel.
 15. Themethod as recited in claim 13 wherein both said anchor and said channelare generally rectangular in cross sectional shape.
 16. The method asrecited in claim 15 wherein said anchor tends to straighten from itshelical configuration, the tendency to straighten urging said anchorinto said channel and maintaining the position thereof.